They cannot refuse a "request" from congress. Even the president must send a representative to answer questions when congress invites him to testify. TSA should be defunded and DHS should be eliminated.

Q: How many terrorists has the TSA stopped?

A: ZERO!

Quoting: Epic Beard Guy

If any of us here resisted attending a congressional hearing we would be arrested and thrown in jail.

People at the TSA can shrug their shoulders submit a piece of paper and essentially tell congress to piss off. Congress then responds, "Okay TSA. Thanks...and sorry to be such a bother!"